Predicting population status of freshwater pearl mussel (Margaritifera margaritifera, L.) in central Sweden using instream and riparian zone land‐use data

Abstract

1. The freshwater pearl mussel Margaritifera margaritifera (L.) has become scarce and threatened throughout most of its distribution range, and is consequently listed as 'endangered' by the IUCN. It has been suggested and used as an indicator species and even as an umbrella species. Despite this, few studies have examined factors affecting its catchment-level population status.2. This work tested the hypothesis that it is possible to predict freshwater pearl mussel population viability (reproducing/not reproducing) and population status in central Sweden from a combination of geospatial data describing riparian land-cover and use, water chemistry data, and electrofishing data describing the abundance of the host fish species (brown trout, Salmo trutta) in 56 streams.3. Mussel population viability was best predicted by total phosphorus. Using higher-resolution data (six classes) on mussel population status, host fish abundance (0+ trout) was the best predictor. At abundances below 5 0+ trout per 100 m 2 and above a concentration of 8 mg L -1 total phosphorus, only three viable populations existed.4. Geospatial data could be used to predict levels of total phosphorus and thereby indirectly to predict mussel viability. Geospatial data could not be used to predict abundance of 0+ trout, which is thought to depend more on instream factors. This study demonstrates that geospatial data on riparian land-use and cover can be a useful tool for screening waters potentially harbouring non-reproducing mussel populations.

Sedimentation affects emergence rate of host fish fry in unionoid mussel streams

“…Brown trout often occur in pearl mussel streams even if juvenile mussels are absent (Geist, Porkka & Kuehn, ; Degerman et al ., ). This may be because trout can survive the eggs stage, although at reduced numbers as was shown in the present investigation.…”

“…This is because sedimentation can cause a combined effect on two life cycle stages of the mussel, namely, (1) reduced total number of glochidia infestations caused by low recruitment and density of juvenile brown trout (Österling et al ., ) and (2) low survival of the newly released juvenile mussels during summer (Geist & Auerswald, ; Österling et al ., ). The positive relationship between the emergence rate of yolk sac fry and juvenile mussels in the present investigation, and results from previous investigations on brown trout and juvenile mussel recruitment (Arvidsson et al ., ; Degerman et al ., ) indicates such strong combined effects of sedimentation on mussel recruitment.…”

“…High sedimentation results in low survival of newly released juvenile mussels during summer, but can also negatively affect egg survival and emergence of brown trout fry during the winter period (Chapman, ), leading to reduced recruitment of juvenile brown trout (Soulsby, Malcolm & Youngson, ; Malcolm, Youngson & Soulsby, 2003b). Juvenile brown trout are considered an important host for the freshwater pearl mussel, and low density of juvenile brown trout has been related to low mussel recruitment (Arvidsson, Karlsson & Österling, ; Degerman et al ., ). Thus, habitat degradation such as sedimentation may have negative effects on M. margaritifera through both reduced juvenile mussel survival and low juvenile brown trout density.…”

The influence of the landscape structure within buffer zones, catchment land use and instream environmental variables on mollusc communities in a medium‐sized lowland river

“…Changes in the landscape structure and land use within riparian zones, even a change from a deciduous forest to a coniferous forest in the river catchment, can significantly reduce populations of freshwater molluscs. Data concerning both instream and riparian zone land use are useful tools for the evaluation of the population status of freshwater molluscs, including endangered species (Degerman et al 2013). The world's freshwater molluscan fauna is facing unprecedented threats from habitat loss and degradation, introduced fish and other pests.…”

Assessing near‐bed velocity in a recruiting population of the endangered freshwater pearl mussel (Margaritifera margaritifera) in Ireland

“…Margaritifera has undergone very serious decline over the last century through catchment intensification, direct river modifications, and pearl fishing resulting in extinction of some populations and inadequate recruitment of young in others (Bauer, 1986;Geist, 2010;Moorkens, 2010). Key remaining strongholds include Scandinavia, Russia, Scotland and Ireland (Cosgrove and Hastie, 2001;Hastie et al, 2003;Geist, 2010;Moorkens, 2010;Degerman et al, 2013). The endangered nature of the animal has led to it being listed in Annex II and Annex V of the EC Habitats Directive (Council of the European Communities, 1992).…”